1. Field of the Invention
The present invention relates to a method for dynamically adjusting the writing speed of a compact disk (CD) drive, and in particular, relates to a method for dynamically adjusting the writing speed in accordance with the data error rate of the data to be written onto a disk.
2. Description of the Prior Art
The current writing speed of laser compact disks that may be burned (i.e., written) once (CD-R) in CD drives that are available on the market has reached 24×, and a continued increase in the writing speed for future CD drives is expected. However, compact disks made by different manufacturers do not have completely identical features, so that the data writing conditions can also be different at the same write speeds. At a given data write speed, it is possible that the compact disk of one brand is able to completely and correctly carry out the data writing action, while the compact disk of another brand may experience problems. For example, data may be omitted, or read outs may be impossible even though the writing is completed, among other unexpected situations.
When a compact disk is made in a factory, a helical pregroove is carved onto its surface, which covers the whole disk from an inside circle radiating outwardly at an interval of about 1.6 micrometers. Taking a 12 cm disk as an example, the groove will cover the whole disk with about 20,000 circles. An optical head is guided by means of this groove to radiate a laser beam on to the groove with the result that a sequence of pits and lands of different patterns are formed, with the patterns of the pits and lands obtained in accordance with codes of the data to be written. The groove is carved with some slight wobbles, by which the whole helical groove is etched in continuous time. By analyzing the wobble groove, the absolute time in pregroove (ATIP) of the compact disc can be obtained. ATIP is well-known in the art, and essentially provides information about the minute, second and frame being accessed or written. In other words, ATIP functions like an addressing means.
Using the obtained ATIP, it is possible to determine (i) the starting point for the time when the writing operation is carried out, and (ii) the ending point for the time available for the writing. For example, a location that is about 25 mm from the axis of the compact disk is approximately the zero point of the ATIP of the compact disk (i.e., 00 min, 00 sec, 00 block). The total duration of the ATIP is the total writable time of the compact disk that can generally be seen on the compact disk. However, this duration changes along with the linear velocity of the compact disk when the compact disk is spinning. As an example, when the linear velocity of a compact disk is 1.2 m/sec, the total time available for writing on this compact disk is about 74 min. When the linear velocity of the compact disk is increased to 1.4 m/sec, the total time available for writing on this compact disk is reduced to only about 64 min.
Even though the ATIP provides some information (such as the starting and ending points for data writing and the like), it does not provide certain relevant information. For example, ATIP does not provide information about the optimum writing speed needed by the compact disk to correctly and completely write data, and whether or not the data can be correctly read after the writing process is completed. As a result, when the CD drive is carrying out the data writing process, it must rely completely on the writing speed specified by the user. This can result in failure of the entire writing process and the subsequent waste of compact disks. For example, if a user selects a speed of 24× for writing to a disk, but the disk is only a 16× disk, the writing operation may fail, or the quality of the written data may be poor. This is because the 16× disk cannot support a writing speed of 24×.
Thus, there still remains a need for a method for adjusting the writing speed of a CD drive to minimize write failures and to improve the quality of the written data.